The everyday build-up of ice upon the surfaces of objects is a familiar annoyance and often a safety hazard. The layers of ice that form on highways, driveways, and walkways make transportation difficult. The masses of ice that accumulate within or upon industrial, agricultural, or other mechanical equipment make operation of the equipment difficult or impossible. The weight of ice on power lines, buildings, wind turbines, refrigeration units, air conditioning and signs often impairs those structures.
Build-up of ice upon the wings and components of an aircraft is of particular concern. The lift generated by the wings, and thus the ability of the aircraft to become and remain airborne, is dependent on the shape of the wings. Even a small accumulation of ice upon the surface of the wings can significantly increase drag and dramatically reduce lift. Further, ice build-up along control surfaces of the aircraft can impede the movement of those surfaces.
There are a large variety of techniques used to control the build-up of ice upon the wings and other surfaces of aircraft. For instance, the aircraft may be deiced before take-off by radiant heat energy or by application of a chemical spray which melts the ice from the wings. Such deicing sprays are not an environmentally preferred solution. The ritual of deicing is well known to airline passengers traveling through cold environments.
Another method of deicing aircraft on the ground or in the air includes providing flexible pneumatic coverings (bladders) along the leading edges of the wings, and supplying bursts of air or fluid to expand the flexible coverings to break away any overlying ice. Similarly, bleeding air from the aircraft engine and routing the heated air to the surface of the wing heats the wing and melts the ice. Ice may also be removed from the wing by providing mechanical energy to the wing, such as through the use of electrically actuated thumpers, which causes the wing to vibrate, fracturing any accumulated ice or by the use of electric blankets.
Although the previously mentioned methods of ice removal are generally effective, they require the continuous supply of air, chemicals, or electrical power in order to rid the wing of its burden. It would be preferred, of course, to reduce the adhesion of ice in the first place.
One might expect that known non-stick coatings would be able to reduce ice from adhering to the surfaces which they coat. It has been found that aluminium surfaces coated with a polytetrafluoroethylene material do show a reduction in adhesion (aluminium 1576 kPa, Teflon 238 kPa), but not as much as might be expected. Further, upon repeated freezing, the favourable properties exhibited by polytetrafluoroethylene and similar coatings can degrade, resulting in a coating with little or no anti-icing capacity.
There is a need for a method which provides a durable surface with low ice adhesion properties and/or delayed freezing, which eliminates or at least reduces the continuous supply of air, chemicals or electrical power in order to reduce the amount of ice forming on a surface and/or the adhesion of ice to the surface.